The Respiratory System
• Cells continually use O2
& release CO2
• Respiratory system
designed for gas
exchange
• Cardiovascular system
transports gases in blood
• Failure of either system
– rapid cell death from O2
starvation
Human Lungs
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Respiratory System Anatomy
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Nose
Pharynx = throat
Larynx = voicebox
Trachea = windpipe
Bronchi = airways
Lungs
Locations of infections
– upper respiratory tract is above vocal cords
– lower respiratory tract is below vocal cords
Trachea
• Size is 5 in long & 1in diameter
• Extends from larynx to T5 anterior to the
esophagus and then splits into bronchi
• Layers
– mucosa = pseudostratified columnar with cilia & goblet
– submucosa = loose connective tissue & seromucous
glands
– hyaline cartilage = 16 to 20 incomplete rings
• open side facing esophagus contains trachealis m. (smooth)
• internal ridge on last ring called carina (cough reflex)
– adventitia binds it to other organs
Histology of the Trachea
• Ciliated pseudostratified columnar epithelium
• Hyaline cartilage as C-shaped structure closed by
trachealis muscle
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Trachea and Bronchial Tree
Airway Epithelium
• Ciliated pseudostratified columnar epithelium with goblet
cells produce a moving mass of mucus.
Bronchi and Bronchioles
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Primary bronchi supply each lung
Secondary bronchi supply each lobe of the lungs (3 right + 2 left)
Tertiary bronchi supply each bronchopulmonary segment
Repeated branchings called bronchioles form a bronchial tree
Histology of Bronchial Tree
• Epithelium changes from pseudostratified ciliated
columnar to nonciliated simple cuboidal, and
finally to simple squamous as pass deeper into
lungs
• Incomplete rings of cartilage replaced by rings of
smooth muscle & then connective tissue
– sympathetic NS & adrenal gland release epinephrine
that relaxes smooth muscle & dilates airways
– asthma attack or allergic reactions constrict distal
bronchiole smooth muscle
Lobules
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Structures within a Lobule of Lung
• Branchings of single
arteriole, venule &
bronchiole are wrapped by
elastic CT
• Respiratory bronchiole
– simple squamous
• Alveolar ducts surrounded
by alveolar sacs & alveoli
– sac is 2 or more alveoli
sharing a common opening
Histology of Lung Tissue
Photomicrograph of
lung tissue showing
bronchioles, alveoli
and alveolar ducts.
Cells Types of the Alveoli
• Type I alveolar cells
– simple squamous cells where gas exchange occurs
• Type II alveolar cells (septal cells)
– free surface has microvilli
– secrete alveolar fluid containing surfactant
• Alveolar dust cells
– wandering macrophages remove debris
Alveolar-Capillary Membrane
• Respiratory membrane = 1/2 micron thick
• Exchange of gas from alveoli to blood
• 4 Layers of membrane to cross
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alveolar epithelial wall of type I cells
alveolar epithelial basement membrane
capillary basement membrane
endothelial cells of capillary
• Vast surface area = handball court
Details of Respiratory Membrane
Double Blood Supply to the Lungs
• Deoxygenated blood arrives through pulmonary trunk from the right
ventricle
• Bronchial arteries branch off of the aorta to supply oxygenated blood to
lung tissue
• Venous drainage returns all blood to heart
Breathing or Pulmonary Ventilation
• Air moves into lungs when pressure inside
lungs is less than atmospheric pressure
– Increase volume of lungs, Boyle’s law
• Air moves out of the lungs when pressure
inside lungs is greater than atmospheric
pressure
– Passive process
• Atmospheric pressure = 1 atm or 760mm Hg
Boyle’s Law
• As the size of closed container decreases, pressure
inside is increased, inverse relationship
• The molecules have less wall area to strike so the
pressure on each inch of area increases.
Dimensions of the Chest Cavity
• Breathing in requires muscular activity & chest size changes
• Contraction of the diaphragm flattens the dome and increases the
vertical dimension of the chest
• Contraction of external intercostal muscles elevates ribs and increases
diameter of chest
Inspiration
• Diaphragm moves 1 cm & ribs lifted by muscles
• Intrathoracic pressure falls and 2-3 liters inhaled
Expiration
• Passive process with no muscle action
• Elastic recoil & surface tension in alveoli pulls inward
• Alveolar pressure increases & air is pushed out
Summary of Breathing
• Alveolar pressure decreases & air rushes in
• Alveolar pressure increases & air rushes out
Alveolar Surface Tension
• Thin layer of fluid in alveoli causes
inwardly directed force = surface tension
– water molecules strongly attracted to each other
• Causes alveoli to remain as small as
possible
• Detergent-like substance called surfactant
produced by Type II alveolar cells
– lowers alveolar surface tension
– insufficient in premature babies so that alveoli
collapse at end of each exhalation
Pneumothorax
• Pleural cavities are sealed cavities not open
to the outside
• Injuries to the chest wall that let air enter
the intrapleural space
– causes a pneumothorax
– collapsed lung on same side as injury
– surface tension and recoil of elastic fibers
causes the lung to collapse
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Lung Volumes and Capacities
• Tidal volume = amount air moved during quiet breathing
• MVR= minute ventilation is amount of air moved in a minute
• Reserve volumes ---- amount you can breathe either in or out above
that amount of tidal volume
• Residual volume = 1200 mL permanently trapped air in system
• Vital capacity & total lung capacity are sums of the other volumes
Dalton’s Law
• Each gas in a mixture of gases exerts its
own pressure
– as if all other gases were not present
– partial pressures denoted as p
• Total pressure is sum of all partial pressures
– atmospheric pressure (760 mm Hg) = pO2 +
pCO2 + pN2 + pH2O
External Respiration
• Gases diffuse from areas
of high partial pressure to
areas of low partial
pressure
• Exchange of gas between
air & blood
• Deoxygenated blood
becomes saturated
• Compare gas movements
in pulmonary capillaries
to tissue capillaries
Internal Respiration
• Exchange of gases between
blood & tissues
• Conversion of oxygenated
blood into deoxygenated
• Observe diffusion of O2
inward
– at rest 25% of available O2
enters cells
– during exercise more O2 is
absorbed
• Observe diffusion of CO2
outward
Hemoglobin
4 heme molecules each bind one oxygen molecule
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Oxygen Transport in the Blood
• Oxyhemoglobin contains 98.5% chemically
combined oxygen and hemoglobin
– inside red blood cells
• Does not dissolve easily in water
– only 1.5% transported dissolved in blood
• Only the dissolved O2 can diffuse into tissues
• Factors affecting dissociation of O2 from
hemoglobin are important
Carbon Dioxide Transport
• 100 ml of blood carries 55 ml of CO2
• Is carried by the blood in 3 ways
– dissolved in plasma
– combined with the globin part of Hb molecule
forming carbaminohemoglobin
– as part of bicarbonate ion
• CO2 + H2O combine to form carbonic acid that
dissociates into H+ and bicarbonate ion
Smokers Lowered Respiratory Efficiency
• Smoker is easily “winded” with moderate
exercise
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nicotine constricts terminal bronchioles
carbon monoxide in smoke binds to hemoglobin
irritants in smoke cause excess mucus secretion
irritants inhibit movements of cilia
in time destroys elastic fibers in lungs & leads to
emphysema
• trapping of air in alveoli & reduced gas exchange
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